Puzzle: doubly truncatable primes
Tom Marlow, from Saffron Walden in Essex, has been looking at the obscure subject of doubly truncatable primes. For example, taking the prime 1373 (and allowing...
Tom Marlow, from Saffron Walden in Essex, has been looking at the obscure subject of doubly truncatable primes. For example, taking the prime 1373 (and allowing 1 to be classed as a prime number) he finds that successively curtailing it first from the left and then from the right, produces the series 373 73 3, 137 13 and 1.



Infographic: Future-proofing UK technology
The current potential of the UK technology industry is restricted by the lack of tech and digital talent available. Read through this challenge for the future of UK business and our economy.
By submitting your personal information, you agree that TechTarget and its partners may contact you regarding relevant content, products and special offers.
You also agree that your personal information may be transferred and processed in the United States, and that you have read and agree to the Terms of Use and the Privacy Policy.
These six extra numbers are all prime, so Tom has designated 1373 as a seven-fold prime. Strangely enough, if these four digits are rearranged to give firstly 3137, and secondly 7331, then in both cases double truncation provides a series of primes. So these two new numbers are also seven-fold in character. These three four-digit primes seem to be the only ones of their size that have this property.
All this leads to Mr Marlow asking: "Which is the only five-digit prime that is double truncatable, ie to provide a nine-fold property?"
Click here for the solution
Read more on IT strategy
-
Computer Weekly @ 50: The future of us – how the next 50 years of tech will reshape the world
-
UKTech50 Video: Digital and corporate IT— Reckitt Benckiser
-
UKTech50 Video: What can The Lego Movie teach us about innovation – Starbucks
-
CWwomen: Research findings into the marketplace – Capability Jane and BP
Start the conversation
0 comments